L’isoprostano PGF2α induce stress del reticolo endoplasmatico ed apoptosi dei macrofagi presenti nelle placche aterosclerotiche carotidee

ISOPROSTAN PGF2α INDUCED ENDOPLASMIC RETICULUM STRESS AND MACROPHAGE APOPTOSIS IN HUMAN ATHEROSLCEROTIC PLAQUES Atherosclerosis is a chronic inflammatory disease that begins asymptomatic, whose progression events may cause acute ischemic stroke and sudden death, and is widely recognized thet endothelium, inflammation and oxidative stress play a key role in all its phases. The progression of atherosclerosis leading to plaque formation with high risk of rupture (unstable plaques), characterized by thin fibrous cap, intimal macrophage infiltration and large lipid core. Recent studies suggest that apoptosis is significantly increased at the point of plaque rupture in patients with acute coronary syndrome and unstable plaques, compared with stable plaques. In animal models, it has been suggested that the expansion of the lipid core is the result of an accelerated macrophage apoptosis, coupled with defective phagocytic clearance, a process called defective efferocytosis. In advanced plaques, in fact, apoptotic smooth muscle cells and apoptotic macrophages not efficiently removed by efferocytosis, accumulate and undergo cell death. In atherosclerotic lesions, several factors seem to contribute to the process of apoptosis of macrophages, and in particular some of these appear to act through the stress of the endoplasmic reticulum (ER). In situations of severe ER stress, when the protective mechanisms activated by unfolded protein response (UPR) are not sufficient to restore normal function of ER, it can trigger the process of cell death by apoptosis. ER stress signaling UPR is triggered by three transmembrane proteins PERK, IRE1 and ATF6, and the transcription factor CHOP may induced apoptosis. In atherosclerotic plaques there are numerous potential sources of ER stress, such as oxidized lipids, unesterified cholesterol, oxysterol (7-keto-cholesterol), isoprostanes (specifically PGF2α) and reactive oxygen species (ROS). A possible role of the enzyme lipoprotein associated phospholipase A2 (Lp-PLA2) in the development and progression of atherosclerosis may derive from its ability to generate, from oxidized phospholipid content in oxLDL, two important pro-inflammatory mediators such as lysophosphatidylcholine (lysoPC) and oxidized non-esterified fatty acids (oxNEFA), in particular isoprostaglandin-like compounds such as PGF2α. The results of this study demonstrate that in the area around the necrotic core, there is an increased presence of apoptotic cells and gene expression of pro-apoptotic proteins, a marked increase in the expression of markers of ER stress and UPR, and the presence of compounds that to induce ER stress and apoptosis (LysoPC, free cholesterol, 7-keto and PGF2α) versus peripheral areas of human carotid plaques. In addition, we demonstrated that an extract of human carotid plaque (PE) is able to reproduce in vitro with THP-1 monocyte-like cell, as detected in advanced lesions of human carotid plaques, induction of a strong expression of factors associated with ER stress and apoptosis. Among the derivatives of the arachidonic acid oxidized content in the PE, produced by activity of Lp-PLA2, the PGF2α powerfully stimulates the ER stress / UPR CHOP-mediated apoptosis, similar to that found with the PE. The PGF2α also determines the production of ROS, which in turn could promote the further radicalization of oxidized membrane phospholipids and oxLDL, an event that could further enhance the ER stress / UPR and apoptosis.